Unstable power supply could cause abnormal system shutdown or data damage during operation of computer equipment, and in serious situations the equipment could be damaged and enormous loss could occur. To prevent such a situation, the computer equipment could be equipped with multiple power supplies to form a redundant power supply system. The redundant power supply system includes two or more power supplies and a back panel. Each power supply provides an output power. The back panel is connected with the power supplies to integrate all output power to drive a load connected to the redundant power supply system. In the event that one of the power supplies malfunctions and an abnormal output occurs, other power supplies share the power needed on the load, and a normal power supply displaces the malfunctioned power supply. Or in the event that the other power supplies have extra power capacity, their output power can be increased temporarily to provide the extra power to the load.
A conventional redundant power supply system, referring to FIG. 1, with two sets of power supplies 1 coupled on a back panel 91 is taken as an example that are connected to a power source 90 to get an input power. The input power passes through a first rectification unit 11 and a power factor correction unit 12 of the power supply 1, and is regulated by at least one power switch 14 controlled by a pulse width control unit 15 and a transformer 13, and passes through a second rectification unit 16 at the secondary side of the transformer 13 to be output to the back panel 91. In order to balance the current output by the two power supplies 1 to the back panel 91, the second rectification unit 16 is coupled at a rear end thereof with a diode 17 to prevent backflow of the current and a current balance unit 18. The current balance unit 18 is connected to the back panel 91. The back panel 91 has a circuit to couple a plurality of current balance units 18. In the event that output currents of the power supplies 1 are unbalance, the current balance unit 18 provides a feedback signal to a power supply feedback unit 19 to provide feedback and regulate output of the pulse width control unit 15, thereby maintain the balance of the output current from the two power supplies 1.
U.S. Pat. No. 7,739,525 discloses a multiple power supplies system with each power supply providing a hot-swappable function. In its FIG. 1, a plurality of power supplies 12a-12d are connected to a current control feedback device 15 in parallel, and include current sensors 20 to regulate output.
U.S. Pat. No. 7,425,779 provides a similar technique with a back panel coupled with a plurality of power supplies to form a redundant power supply system equipped with fault tolerance function.
However, a system to accommodate multiple sets of power supplies and a back panel is costly and bulky, and such a large redundant power supply becomes a waste to a smaller electronic system. In the conventional technique, if multiple sets of power supplies are not integrated through a back panel, output voltages will be slightly different because of small variations of elements even if the specifications of the power supplies are exactly the same. Unbalance of voltage and current will cause the power supply with a higher output voltage be heavily loaded. Such a phenomenon will notably affect the lifespan of the power supply. Integrating multiple sets of power supplies creates difficulty in control of output balance of the power supplies. Thus there is a dilemma in the design of the redundant power supply system in terms of cost and stability.